Of interest to applications in the biopharmaceutical industry are not only sterile end-products for administration, but also sterile materials used in the production of active pharmaceutical ingredients. Here, materials refer to components of the individual process steps and to media. For example, in the production of monoclonal antibodies, even the fermentation step requires a sterile fermentation vessel and sterile media in order to absolutely ensure an appropriate growth of the cell lines. After cell growth and protein biosynthesis, the antibody must be separated in purest possible form from cells and other undesired components. A wide variety of different process steps are used here. After cell removal by depth filtration or centrigation, these generally include a wide variety of different chromatography steps for the concentration and purification of the target molecule, methods for virus removal and also concentration and sterile-filtration steps. During these process steps too, it is advantageous for the operations to be pathogen-free. This can accordingly minimize the risk of contamination of the final product.
A special case is the cleanup of relatively large molecules such as, for example, viruses or virus-like particles: in many cases, sterile-filtration in the work-up is not possible here. Owing to the size of the molecule, sterile filters that are used would retain the product via their pore size and make a filtration procedure impossible. Here in particular, sterile process solutions are a crucial improvement.
In many of the process steps mentioned, it is standard to lower the risk of a contamination by rinsing with alkaline solution or the use of heat. However, these methods have various disadvantages: in many cases, the implementation in the process is complicated. Large amounts of alkaline solution or else hot steam must be provided. A time-consuming cleaning procedure must be carried out before the actual process step. A further disadvantage is, in many cases, the stability of the materials used in the individual process steps. For example, hot steam cannot be used for sterilizing chromatography media. Other materials do not have sufficient stability with respect to alkaline solution.
In recent years, the trend towards using “single-use” products in the production of active biopharmaceutical ingredients has increased. The single use and predominant use of plastics for materials such as filtration devices thus also paved the way to alternative sterilization methods. Besides autoclaving, sterilization methods such as gas treatment with ethylene oxide or gamma irradiation are used. A further advantage arises here for the user also in the availability of pre-sterilized products for the production process. Thus, cleaning efforts for the user can be reduced or completely dropped.
In general, sterilization methods can be divided into chemical and physical methods. In the case of chemical methods, the use of pathogen-eliminating gases is widespread. However, in this method, it must be ensured that all regions of the material come into sufficient contact with the gas during the sterilization. Physical methods are heat-sterilization and irradiation. In this case, the sterilizing action of the irradiation is based on the destruction of organic material by bond cleavage. The advantage of an irradiation procedure is that all regions of a material can be penetrated.
Chromatography media are customarily sanitized. Sanitization refers to, inter alia, the pathogen-reducing treatment with alkaline solution. In many cases, this involves using a solution of up to 1 molar. However, in this connection, this treatment does not result in a sterile product or a sterile process step. Furthermore, a major disadvantage of this treatment method is the manner of provision. Either the effort in relation to the sanitization must be expended directly before the use in the process, or the manufacturer of the chromatographic medium must sanitize the medium in appropriate chromatography devices as early as during production and supply it in the wet state. This complicates not only the handling; it is also necessary to carry out complex studies in relation to the stability in the storage solution. Pre-sanitized products in chromatography are known as “ready-to-use” products.
It is also possible to use autoclaving for sterilization. This involves having to heat the chromatography medium to at least 121° C. However, this method is unsuitable for relatively large scales, since there is no possibility of implementation for the devices owing to the size.
A further method which has been described is the use of hot buffers for sterilization. This involves heating the chromatography medium likewise to at least 121° C. However, a prerequisite therefor is that the chromatography system is stable with respect to a thermal stress and pressure. This method is not suitable for single-use systems.
US 2013/0062267 A1 describes a sterilization method for providing aseptic chromatography columns. However, this involves having to sterilize the medium and the filtration device (chromatography housing) separately and then introducing the chromatography medium with sterilized equipment into the device. Furthermore, the method is only applicable for polymer gels.
Although already sterile single-use fermentation vessels and filtration devices have become established in the area of filtration and fermentation, it has so far not yet been possible for readily available sterilized products to become established in the application of chromatography. A major reason therefor is the stability of the materials. In this connection, both support matrix and ligand can be damaged by influence of heat, gamma irradiation or other sterilization methods or they are only insufficiently accessible. In chromatography, the support matrices used are, for example, polymer gels, membranes, non-wovens, films or fibres. Ligands can be, inter alia: proteins, substrates, carboxymethyl, sulfonates, quaternary amines, aminoethyl, metal chelates or hydrophobic groups. In this connection, the irradiation of the materials can, for example, damage or detach the side chains of polymers. A treatment with oxidative media such as with reactive ethylene oxide can similarly lead to an alteration of the ligands.
The sterilization methods known in the prior art demonstrably lead to a change in the material properties, as can be seen directly on discolorations of the chromatography material for example. Although such discolorations need not necessarily be adverse in terms of the production contamination in the process, they may nonetheless be undesired, as described in US 2011/0064608 A1 for example.